BOSTON — When scientists made the stunning announcement last year that a baby born with H.I.V. had apparently been cured through aggressive drug treatment just 30 hours after birth, there was immediate skepticism that the child had been infected in the first place.

But on Wednesday, the existence of a second such baby was revealed at an AIDS conference here, leaving little doubt that the treatment works. A leading researcher said there might be five more such cases in Canada and three in South Africa.

And a clinical trial in which up to 60 babies who are born infected will be put on drugs within 48 hours is set to begin soon, another researcher added.

If that trial works — and it will take several years of following the babies to determine whether it has — the protocol for treating all 250,000 babies born infected each year worldwide will no doubt be rewritten.